1Advanced Ultrafast Laser Research Center and the Department of Engineering Science, Faculty of Informatics and Engineering, Department of Engineering Science, The University of Electro-Communications, 1-5-1, Chofugaoka, Chofu, Tokyo 182-8585, Japan

Abstract

We have developed an experimental system for real-time vibrational spectroscopy of molecules in a specific electronic excited state. A synchronized UV light source and a few-cycle visible laser pulse were utilized to prepare and investigate the ultrafast dynamics of molecules in the electronic excited states. A multichannel lock-in amplifier detection system operating in a tandem double lock-in detection mode was used to extract the signal correlated only to the UV and visible pump pulses. Real-time vibrational spectroscopy of chrysene in the triplet state and 1′, 3′-dihydro-1′, 3′, 3′-trimethyl-6-nitrospiro [2H-1-benzopyran-2, 2′-(2H)-indole] in a photochromic state was demonstrated.

The double-laser systems were composed of a femtosecond regenerative amplifier system (Legend-USP, Coherent, Inc.) and a picosecond regenerative amplifier system (Legend-P, Coherent, Inc.). The timing firing the Q switch and SDG was tuned by the digital delay generator (DG535, Stanford Research). The timing signal was detected by the FPD-510-FV (Menlo Systems, Inc.) The feedback stage (FS-1020X, Sigma Tech, Inc.) was used to tune the pump’s optical delay. The modulation for the probe pulse was created by the chopper (Model 3501, New Focus, Inc.) and shutter (SH05, Thorlabs, Inc.). The MLA system was composed of fibers (FiberTech Optica, Inc.), a polychromator (SpectraPro2300i, Acton Research, Inc.), APDs (S5343, Hamamatsu Photonics, Inc.), preamplifier (7210/90, Signal Recovery, Inc.), and an MLA (7210, Signal Recovery, Inc.). The resistor tunable low-pass filter kit was used to reduce the unwanted higher frequency components of the signal (SR-4FL2, NF Corporation, Inc.).

Other (4)

The double-laser systems were composed of a femtosecond regenerative amplifier system (Legend-USP, Coherent, Inc.) and a picosecond regenerative amplifier system (Legend-P, Coherent, Inc.). The timing firing the Q switch and SDG was tuned by the digital delay generator (DG535, Stanford Research). The timing signal was detected by the FPD-510-FV (Menlo Systems, Inc.) The feedback stage (FS-1020X, Sigma Tech, Inc.) was used to tune the pump’s optical delay. The modulation for the probe pulse was created by the chopper (Model 3501, New Focus, Inc.) and shutter (SH05, Thorlabs, Inc.). The MLA system was composed of fibers (FiberTech Optica, Inc.), a polychromator (SpectraPro2300i, Acton Research, Inc.), APDs (S5343, Hamamatsu Photonics, Inc.), preamplifier (7210/90, Signal Recovery, Inc.), and an MLA (7210, Signal Recovery, Inc.). The resistor tunable low-pass filter kit was used to reduce the unwanted higher frequency components of the signal (SR-4FL2, NF Corporation, Inc.).

(a) 2D plot of ΔΔA(ω,t) of chrysene in the triplet state. The contour means the intensity from −0.0005 (blue) to 0.0005 (red). (b) Integrated real-time traces of ΔΔA(ω,t) for the wavelength range of 540 to 580nm. (c) ΔΔA(ω,t) as a function of wavelength at a delay time of 300fs.